UV curing coatings have been developed during the 1970s. It is an environmentally friendly green technology with many advantages. No environmental pollution is caused because of no organic solvent evaporated during curing. At the same time, it can reduce energy waste during curing, shorten the production time, and the quality is much easy to control.
In the beginning, UV cured inks are not acceptable in industry. Along with development of photoinitiators and diluents with bifunctional group or multi-functional group, UV cured inks are gradually acceptable at last Besides wide raw material sources allowing easy preparation of UV coatings with difference properties by factories, photoinitiation of UV curing provides a fast curing process and shorter production time. The curing reaction is carried out according to user's requirements so that preparation process is more flexible. Moreover, the UV cured ink contains no organic solvent and no heating is required. These features make processing of heat-sensitive electronic materials in the clean room become feasible.
Generally, the UV cured ink includes three main components. The first is oligomer that features on no odor, excellent curing property and low toxicity. The oligomer is a prepolymer comprising multiple repetitions of units and having molecular weight between small molecular monomer and high molecular polymer. The oligomer is a main chemical involved in photo curing and having great effects on various properties of the cured ink including mechanical property, chemical property, physical property, etc.
The second component is reactive monomer which features on photo-reactivity, good curing rate and low viscosity. Due to low molecular weight and low viscosity of the monomer, the reactive monomer can replace the solvent to be added in to oligomer and used as a diluent. Thus the viscosity of the ink is reduced and is easy to be processed. The most common used reactive monomers include vinyl monomer, propenyl monomer, and acrylic acid monomer. According to the number of functional group contained, the monomer can be divided into two groups-one is monomer with single functional group while the other is monomer with multiple functional groups. The monomer having a single functional group is with lower molecular weight and used as a diluent for viscosity reduction and modification of physical properties of cured body. Yet it's less used now due to high volatility and bad smell. As to the monomer with multiple functional groups, it has faster reaction rate and higher crosslinking density. Thus the hardness after curing is higher.
The third is photoinitiator that features on absorption of UV radiation energy, initiation of polymerization, and good thermal stability. The active form of the photoinitiator varies according to the structure, divided into two groups-free radicals and radical cations. After absorbing UV light, free radicals or radical cations are generated and react with monomers as well as corresponding oligomer to carry out chain polymerization reaction. The composition and concentration of the photoinitiator have great effects on the time required for curing and the wavelength range in which the photoinitiator absorbs light.
Besides the above three main components, additive and color pigments for inks can also be used due to various requirements of ink performance and applications. The additive used is for achieving certain property or reducing operational flaws. The present invention features on that a novel aluminum chelate and a method for manufacturing the same are provided. After the novel aluminum chelate being added into photo cured inks, the properties of the photo cured inks are improved significantly.